A CLIMATIC INDEX FOR SOIL-EROSION POTENTIAL (CSEP) INCLUDING SEASONAL AND VEGETATION FACTORS

The concept of Cumulative Erosion Potential (CEP) proposed by De Ploey, Kirkby and Ahnert in 1991 (Earth Surf: Process. Landforms, 16:399-409) provides a simple climatic index of erosion potential based on annual rainfalls and their distribution, which is assumed to be exponential (or gamma with shape parameter 1). A modified CEP (CSEP) is presented here, extending the original in three ways. First, the index is disaggregated by month to include the effects of seasonality. Second, a mixed gamma(1) distribution is used to provide a better fit to the whole of the daily rainfall distribution. Third, the index is calculated both for a bare soil and for a natural vegetation cover, giving an additional index to the potential for managing erosion through landuse change. For the natural vegetation, the index is based on an estimate of equilibrium soil organic matter which is associated with differences in soil moisture storage capacities and derived from monthly rainfall and temperature values. The index thus remains a measure of climatic potential only, based on widely available monthly data on temperature, rainfall and number of rain days. It may be compared with the patterns shown by the European Soil Erosion Map and by the CORINE classification, which are dominated by a combination of climate and lithology.